Interlocking corner construction for corrugated paper board boxes



May 12, 1970 w. c. CHUBER EIAL 3,511,430

INTERLQCKINGCORNER CONSTRUCTION FOR CORRUGATED PAPER BOARD BOXES Filed May 17, 1968 v 2 Sheets-Sheet 1 INVENTORS WILLIA 0.0HUBER GERRYVLJORDAN ATTORNEY y 2, 1970 w. c. CHUBER ETAL INTERLOCKING CORNER CONSTRUCTION FOR CORRUGATED PAPER BOARD BOXES Filed May 17, 1968 2 Sheets-Sheet 2 12 FIG.6

ATTORNEY United States Patent 3,511,430 INTERLOCKING CORNER CONSTRUCTION FOR CORRUGATED PAPER BOARD BOXES William C. Chuber and Gerry W. Jordan, Statesville, N.C., assignors to International Paper Company, New

York, N.Y., a corporation of New York Filed May 17, 1968, Ser. No. 730,049

Int. Cl. B65d 5/26 US. Cl. 229-35 5 Claims ABSTRACT OF THE DISCLOSURE A corner construction for corrugated paper board boxes having an interlocking tab and cut wherein an edge of the cut and an edge of the tab are in abutting engagement along a line normal to the knockdown path of the tab carrying side and wherein the tab receiving cut extends to the upper edge of the corner to facilitate erection.

This invention relates generally to interlocking corner constructions for boxes made from a unitary blank of corrugated paper board. This type of construction pro vides for the erection of boxes without adhesives or wire stitching.

An example of a folding box of this type is a box used for the transportation of live chicks, however, the construction should not be inferred as being limited to this type of box. The live chick box is normally provided with reentrant sides to provide ventilation for the chicks when the boxes are stacked. This type of box requires great stacking strength to protect its live contents and also must be of a type which can be rapidly erected without auxiliary equipment.

Folding boxes of the type mentioned are normally provided with looking tabs which are articulated to the sides of the box. T 0 provide the necessary strength it is conventional to utilize tabs which are inserted into slits that are surrounded by board. This type of lock inhibits rapid erection.

It has been found that the most rapid erection can be achieved where the slit into which the lock is placed runs to the upper edge of the erected side panel of the box. Also the tabs should extend to the edge of the sides to which they are attached. In this manner the tab and the slit are readily available without the necessity of pushing either very far out of a surrounding plane of board. Hitherto, locks so constructed have not provided an interlock which is sufficiently positive.

Another desirable characteristic is ready interlocking of the flap and slit as a natural consequence of the motions involved in erecting the box from the blank. Assuming that the lock tabs are articulated to the ends of the box, and that the sides of the box which contain the tab receiving cut have been rotated to their upright position, the locking tabs should enter the tab receiving cuts as a natural consequence of rotating the ends of the box to their upright position. Furthermore, the tabs should lock with the cut automatically as soon as the tab ends reach their upright position without further manipulation or distortion of the box. There should be no necessity to push the ends beyond their normal erected position to achieve a lock and there should be no necessity to handle the locking tab once it starts to enter the tab receiving cut.

In the instant invention a corner construction is provided wherein the tab receiving cut extends to and intersects the upper edge of one of the side panels of the box for ready access, so that the locking tab readily engages the cut as the box is erected, rotating directly into the cut as the adjacent side panel is rotated to the upright position. Furthermore, the lock is so. positive that the board must be torn or severely distolted to free the lock.

Since all of the corners of the box may have the same construction, if desired, only one corner will be described, this being sufficient to understand fully the invention herein set forth. The corner comprises a portion of the bottom panel of the box having two adjacent intersecting primary fold lines at which are articulated a pair of adjacent upright side panels. In accordance with this invention, a corner construction is provided with a locking cut in one of the adjacent side panels which is spaced from the corner of the box and, in the preferred embodiment, has a first cut portion which proceeds downwardly, parallel to the corner edge from the upper edge of the one side panel and is further provided at the bottom of such parallel portion with a bottom cut position which angles downwardly toward the corner. Such one wall has attached thereto a stiffening flap articulated at a secondary fold line at the corner. When the box is erected the stiffening flap lies parallel to and inside the adjacent side of the box. The fold line of this flap defines the corner edge. This flap also provides rigidity to the side panel containing the slit. The bottom edge of the flap bears against the bottom panel and biases the one side panel away from its erected position and thus places locking pressure on the interlock.

The other adjacent side panel carries the locking flap.

The flap is articulated at its proximal side to the other side panel along a locking flap fold line, which folds around the outside of the corner edge of the box. The flap is provided with a tab defining slit which, in the preferred embodiment, has a second portion generally parallel to the bottom of the box. The second portion must be spaced from the bottom by an amount at least equal to the spacing from the intersection of the primary fold lines of the bottom of the tab receiving cut. Due to the thickness of the corrugated board, slightly greater spacing is desirable. The second portion proceeds from its intersection with the distal edge of the tab to a point slightly above the bottom of the tab receiving cut when the box is erected. The tab forming slit has a first portion which proceeds from the proximal end of the second portion upwardly and away from the corner in register with the bottom portion of the tab receiving cut when the box is erected. The second portion of the slit then projects upwardly in register with at least part of the first portion of the tab receiving cut but stops short of the top of the tab receiving slit. The tab is thus generally defined by the tab defining slit and the upper distal edge of the looking flap, being connected to the locking flap by the paper board between the top of the first portion of the slit and the upper edges of the locking flap.

The result of the shape of the tab forming slit is a tab having a wedge shaped foot which points toward its respective corner. When interlocked, the slanted upper face of the foot defined by the distal edge of the slit abuts the slanted portion of the tab receiving cut defined by the proximal edge of the cut. Due to the orientation of the abutting surfaces the area of contact is approximately normal to the path the tab would follow if the side to which it is articulated were rotated into the downward position. As a further result of this orientation it is not necessary to have a portion of the tab deliberately project beyond the slit to have positive engagement. This means that the tab does not have to be greatly flexed to enter the slit and provide a lock, nor does the other side panel have to be pushed beyond its normal erected position so that locking engagement is achieved. Since the other side panel does not have to be pushed beyond its normal erection position, it is not necessary to provide clearances for this purpose. Thus, firm abutment of the corner elements is possible providing a more rigid corner. The locking tab merely enters the slit as the box is erected and when the slanted surface of the foot and the second portion of the tab engaging cut are in register, the natural biasing action of the walls surrounding the cut will force the foot to move inwardly with respect to the box, thus causing the two registered surfaces to abut. The walls surrounding the cut act like the blades of a scissors. This relation is maintained by the biasing action of both the walls surrounding the tab receiving cut as well as by the biasing action of the board surrounding the tab defining slit. In particular, the area of the one side wall between the tab receiving cut and the stiffening flap is more rigid than the area on the distal side of the cut. It is also more rigid than the board on either side of the tab defining slit. Thus, during locking, the area between the cut and the stiffening flap remains close to its original plane. This has the effect of increasing the area of abutment of the distal tab edge and the :proximal edge of the cut, since they will remain more nearly in the same plane. Furthermore, the locking flap tends to bias the one side panel inwardly acting against the outward bias provided by the bottom edge of the stiffening flap against the bottom panel. The result is a very rigid corner structure.

While the preferred embodiment calls for a first cut portion parallel to the edge of the box and a second slit portion parallel to the bottom of the box neither of these orientations is essential. For example, it is only necessary that the second slit portion be spaced from the intersection of the two primary fold lines a distance slightly greater than the distance of the bottom of the cut from that intersection. Using such definition, the second slit portion can be an arc whose radius is slightly greater than the distance from the cut to the intersection of the primary fold lines. Similarly, it is the angular relation of the first and bottom cut portions which is significant and they can be connected by a curved portion, or for that matter, the first and/or the second portion could be curved or could constitute a continuous curve.

It is an object of the instant invention to provide a corner lock for corrugated paper board boxes wherein the locking tab will enter the tab receiving cut as a natural consequence of the erection of the box without extensive manipulation of either the tab or the tab receiving cut.

It is another object of this invention to provide a corner lock for corrugated paper board boxes wherein the tab receiving cut is exposed in the upper edge of the corner to provide for ease of entry of the lOCking tab during erection.

It is still another object of the instant invention to provide a corner lock for corrugated paper board boxes wherein locking is achieved by edge to edge abutment of one edge of the tab receiving cut and one edge of the tab along a line normal to the knockdown path of the tab carrying side.

These and other objects will be apparent from the foregoing general description and the following detailed description of the instant invention.

An embodiment of the instant invention is hereinafter described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is a portion of the unitary blank according to the present invention.

-FIG..2 is an isometric representation of the corner construction of the instant invention showing an inside view of the locking fiap entering the tab receiving cut.

FIG. 3 is the corner of FIG. 2 viewed from the outside.

. FIG. 4 is the corner of FIG. 2 with the lock fully engaged.

FIG. Sis a partial plan view of the corner of FIG. 4 with a cross-section--taken along line 55.

FIG. 6 is a partial elevation view of the corner of FIG. -5 with a-cross-sectiontaken along line 6-6.

FIG. 7 is an isometric representation of an erected box using the corner construction of the instant invention.

FIG. 8 is a fragmentary isometric view of the tab receiving out of the instant invention.

FIG. 9 is a fragmentary cutaway isometric view of the tab defining slit of the instant invention.

Unless otherwise stated the corner will be described in its erected state of in the process of being erected. The terms upper, upstanding and bottom are used for descriptive purposes and should not be construed as specific limitations. The terms distal and proximal refer to the relative positions of various elements to the corner edge.

Referring now to the details of the invention, the blank 10 shown in FIG. 1 is a unitary blank formed from corrugated paper board. The blank comprises a bottom panel 12 having primary fold lines 14 and 16 at two intersecting adjacent edges. A pair of adjacent side panels 18 and 20 are articulated at primary fold lines 14 and 16. The side panels 18 and 20 have upper side panel edges 22 and 24 respectively and adjacent ends 26 and 28 respectively.

One side panel 18 carries a stiffening flap 30 articulated to end 26 along secondary fold line 32 which extends from substantially adjacent the bottom panel 12 to the upper edge 22. The stiffening flap has a bottom edge 34 which, in the erected corner abuts bottom panel 12 adjacent fold line 16 (FIG. 4) providing an outward bias to the outside panel 18. Also, due to its angular relationship to the one side panel 18, a high degree of stiffening of side panel 18 is achieved in the vicinity of fold line 32. The other side panel 20 provides biasing force to retain the stiffening flap in position against it.

The other side panel 20 has attached thereto a locking flap 36 adjacent its upper edge 24 and articulated to the other adjacent end 28 along locking flap fold line 38. Although it would be permissable for the locking flap to extend the length of other end 28, it is not necessary, however, it is contemplated that the box be made from a unitary blank and since it is more desirable that the stiffening flap extend the full length of the end 26 for reasons already stated, the locking flap 36 extends for only a portion of the length of the other end 28. The locking flap may be described as being defined by its proximal flap edge which is coincident with locking flap fold line 38 and its distal or exposed flap edge 40 which has three sides. The corner when erected has a corner edge 42 (FIG. 3) which is coincident with the outside of secondary fold line 32. The inside of locking tab fold line 38 lies adjacent to and outside corner edge 42, tab 36 being folded around the outside of the corner.

A locking cut 44 is provided in the one side panel 18. This cut receives locking tab 46 which is defined by locking tab slit 48 and the upper portion of distal edge 40.

Locking cut 44 is defined by distal cut edge 50 and proximal cut edge 52 (FIG. 8). It is spaced from said corner edge 42, its first cut portion 56 intersecting upper panel edge 22 at upper panel edge intersection 54 and extending, in the preferred embodiment, downwardly substantially parallel to corner edge 42. It further comprises a dog-leg bottom portion 58, extending downwardly and toward corner edge 42 to a bottom point 60 which is a distance R from the intersection of the primary fold lines 14 and 16 at primary fold line intersection 62.

Tab defining slit 48 which is defined by distal slit edge and proximal slit edge 67 (FIG. 9) comprises a first portion 64 which is in register with the bottom cut portion 58 and the lower part of the first cut portion 56. A second slit portion 66 intersects the first slit portion 64 at slit intersection 68. Intersection 68 is spaced slightly more than the distance R from intersection 62. The second slit portion extends, in the preferred embodiment, parallel to the bottom panel 12, when the box is erected, to distal flap edge intersection 70 at distal locking flap edge 40. The second portion, it should be understood, need only be spaced at least a distance slightly more than R from intersection 62. Thus, it could be an are from intersection 68 to the distal locking flap edge 40 with slightly more than R as its radius and primary fold line intersection 62 as its center. A distance slightly more than R is necessary so that the tab may be received in cut 44. Since the corrugated board has some finite thickness, when the cut is flexed to receive the tab, a portion of the bottom of the cut will not open sufficiently to receive the tab. Therefore, the deepest entry of the tab into the cut must be less than the full depth of the cut. The extra length of the cut necessary may be easily determined by one having reasonable skill in the box art. A wedge shaped foot 72 is formed by the first and second cut portions. The locking tab is attached to the locking flap by the portion of the board between the top of the first cut portion and the distal locking flap edge. Thus, the upper part of the first slit portion, which in the preferred embodiment runs parallel to the locking flap fold line 38 is limited by the strength required in the area of attachment between the locking tab and the locking flap. It should be noted that the angular relationship of the first and bottom portion of the tab receiving cut aids the automatic self-locking ability of the lock.

FIGS. 2 and 3 show the locking flap entering the locking cut. It can be seen that as the other side panel is rotated into its upright position and as the locking flap is urged inwardly against the one side wall during this process the distal edge of the locking flap will naturally enter locking cut 44 without further manipulation. Since the locking cut extends to the outside edge 22 only slight inward urging is necessary to open the cut an amount sufficient to accept the locking flap. This ease of insertion is not possible where the locking cut is surrounded by board.

FIGS. 4, S and 6 show the corner in a fully locked position. The scissor action of the board surrounding the cut will automatically push the wedge shaped foot inwardly and hold it in that position. Thus, the distal slit edge 65 and proximal cut edge 52 are held in abutting relationship. Also, at least a portion of the line of abutment is approximately normal to the path which would be followed by the locking tab if the other side panel were rotated away from the corner. This creates a positive lock, the elements of which will not slip longitudinally with respect to each other which would cause disengagement.

As shown in the preferred embodiment by arrow 74, the alignment of the flutes of the corrugated board which runs parallel to primary fold line 16 provides the greatest resistance to fiexure to both the board surrounding cut 44, the area of attachment of the tab 46 to flap 36 and the board adjacent the second portion of the distal cut edge 67. This flute orientation also insures end to end flute engagement of the proximal cut edge and the distal slit edge which are compressively loaded against each other.

What is claimed is:

1. A folded structure formed from a unitary fiat blank of corrugated paper board comprising a bottom panel, primary fold lines along at least two adjacent intersecting edges of said bottom panel, at least two upstanding side panels having upper edges, adjacent ends, and being articulated to said bottom panel at said primary fold lines, a stiffening flap, a secondary fold line along one of said adjacent ends on one of said side panels, said flap being articulated to said one end at said secondary fold line, said flap extending from substantially adjacent said bottom panel substantially to the upper edge of said one side panel along said secondary fold line and having a bottom edge extending from said secondary fold line, adjacent said bottom, the bottom edge of said stiffening flap having at least a portion, spaced from said secondary fold line, abutting said bottom panel adjacent the primary fold line of said other side panel, said stiffening flap being biased inwardly with respect to the folded structure by said other side panel, said secondary fold line defining one corner edge of said folded structure, a locking fiap defined by a proximal flap side and a distal flap edge, a locking flap line adjacent the upper edge of said other side panel and extending along the other of said adjacent ends, said locking flap being articulated along said proximal flap side to said other end at said locking flap fold line, said locking flap being folded along said locking flap fold line around the outside of said corner edge and having at least a portion thereof lying against the outside of said one side panel, a locking cut in said one said panel defined by distal and proximal cut edges, said out being spaced from said corner edge, intersecting the upper edge of said one side panel and having a bottom cut portion, spaced downwardly from the upper edge of said one side panel, and extending toward said secondary fold line, a tab defining slit in said locking flap defined by distal and proximal slit edges, said slit having a first slit portion in register with at least the bottom out portion, a second slit portion intersecting the bottom of said first slit portion and extending to and intersecting the distal flap edge of said locking flap, said second slit portion being spaced from the intersection of the primary fold lines by an amount slightly greater than the spacing of said bottom cut portion from the intersection of the primary fold lines, a tab in said locking flap at least partially defined by the distal opposed slit edge of said tab defining slit and a portion of the distal flap edge above said slit, said tab being received in said locking cut with said distal edge abutting said proximal cut edge.

2. The structure of claim 1 wherein said locking cut comprises a first cut portion parallel to said corner edge, intersecting the upper edge of said one side panel and extending downwardly to said bottom out portion, said bottom out portion comprising a substantially straight out extending downwardly and toward said corner edge, said first slit portion being in register with said bottom cut portion as well as the bottom part of said first cut portion.

3. The structure of claim 1 wherein said one side panel further comprises a first side panel portion extending between said proximal cut edge and said corner edge, said stiffening flap comprising means to strengthen said first side panel portion and bias said proximal cut edge outwardly with respect to said structure against said locking flap, a second side panel portion extending distally from said distal cut edge inwardly said biasing means comprising a scissor means to bias said tab inwardly to insure locking abutment of at least portions of said proximal cut edge and said distal slit edge.

4. The structure of claim 1 wherein the corrugations in said blank run substantially parallel to said primary fold line of said other side panel.

5. The structure of claim 1 wherein the spaced portion of said slit is substantially parallel to said primary fold line of said one side panel.

References Cited UNITED STATES PATENTS 1,515,983 11/1924 Williams 22935 2,366,419 2/1945 Meller 22935 2,488,705 11/ 1949 Buttery et al. 229-35 2,488,706 11/1949 Buttery et al. 22935 2,660,364 11/1953 Ferguson 229--35 2,712,409 7/1955 Buttery 229-35 3,185,381 5/1965 Fobiano et al. 22935 3,226,006 12/1965 Dunn 22935 DAVIS T. MOORHEAD, Primary Examiner US. Cl. X.R. 229-6 

